A Trickle Does the Trick
Posted: April 1, 2013
I have a battery switch in my 23-foot boat. If I leave the switch on ALL and put a trickle charger on one battery, will it maintain both batteries over the winter if everything else is turned off?
If your boat is wired like a typical four-position battery switch (1, 2, ALL, OFF), placing the switch in the ALL position electrically connects the batteries together, essentially making them one big battery. If you connect a trickle charger to one battery, it will also charge the other. So, while the short answer is yes, it will work, how effective this approach actually is depends on a number of factors, from the output of the trickle charger to the size of the batteries. A better long-term solution would be to install a double-bank smart charger or a single-bank charger and battery combiner (which automatically puts batteries in parallel when it senses charging voltage is present).
If you do go with a trickle charger, use one that senses battery voltage and turns itself off automatically when the batteries are fully charged. If you’re using wet-cell batteries, monitor the electrolyte levels, as they may need periodic topping off over the winter months.
Last, avoid using spring or alligator clips to connect your charger to the batteries, as they can fall off or generate sparks. Spring-loaded clips are OK for emergency charging, but for permanent installations ring terminals are the recommended way to connect charger leads to battery posts